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Victoria University Antarctic Research Expedition Science and Logistics Reports 1993-94: VUWAE 38

Popular Summary of Scientific Work Achieved

page 1

Popular Summary of Scientific Work Achieved

The origin of quartzose sandstones in the lower part (Devonian) of the Beacon Supergroup, southern Victoria Land, Antarctica has generated considerable debate. The controversy centres on the presence of varied and abundant trace fossils, frequently used by some geologists as indicators of marine paleo-environments. However, these same trace fossils have been found by others in nonmarine paleoenvironments. Most previous studies of these sandstones have been conducted on a regional scale and insufficient data has been collected to establish sedimentary processes and depositional environment with confidence.

This study was designed to examine the lowermost Beacon Supergroup in detail. The New Mountain Sandstone at Table Mountain has excellent 3-dimensional exposures, and contains a variety of trace fossils and sedimentary structures. The exposures are ideal for lateral profiling techniques, which take into account lateral as well as vertical fades changes in order to provide a refined depositional model. Improved understanding of the depositional system will contribute not only to resolving the trace fossil problem, but also to southern Victoria Land paleogeographic and tectonic reconstructions.

Detailed examination of the New Mountain Sandstone revealed no evidence of marine deposition. Most of the sandstone was found to be eolian (wind blown), with evidence of water-lain deposition in the upper part. Features which support an eolian environment include climbing translatent strata, pinstripe laminations, adhesion ripples and ripple forms with coarse-grained tops. Thin intervals of trough cross-bedded sandstone represent periodic flooding by braided rivers. Paleowind directions are primarily from the northwest and the rivers flowed towards the northwest. Deposition in the uppermost New Mountain Sandstone was likely in a complex intermixture of eolian and fluvial environments. Features indicative of a water-lain environment include massive sandstones, slumped cross beds, mudcracks, and a change in paleocurrent direction to the northwest.